Yellow light afterglow material and preparation method thereof as well as led illuminating device using same

ABSTRACT

The invention relates to a yellow light afterglow material and a preparation method thereof as well as an LED illuminating device using the same. The yellow light afterglow material comprises the chemical formula of aY 2 O 3 .bAl 2 O 3 .cSiO 2 :mCe.nB.xNa.yP, where a, b, c, m, n, x and y are coefficients, and a is not less than 1 but not more than 2, b is not less than 2 but not more than 3, c is not less than 0.001 but not more than 1, m is not less than 0.0001 but not more than 0.6, n is not less than 0.0001 but not more than 0.5, x is not less than 0.0001 but not more than 0.2, and y is not less than 0.0001 but not more than 0.5; wherein Y, Al and Si are substrate elements, and Ce, B, Na and P are activators. The yellow light afterglow material is prepared by the following steps: weighing oxides of elements or materials which can generate oxides at high temperature by molar ratio as raw materials, evenly mixing and then sintering the raw materials at 1200-1700° in a reducing atmosphere.

FIELD OF THE INVENTION

The invention relates to a yellow light afterglow material and apreparation method thereof as well as an LED illuminating device usingthe same, more particularly to a yellow light afterglow material usingtrivalent Ce as luminescent ions, and B, Na and P as a defect center,and a DC and/or AC LED illuminating device using the afterglowluminescent material.

DESCRIPTION OF THE RELATED ART

The reason for afterglow phenomenon is that materials have defectlevels, the defect levels capture holes or electrons at activationstage, the electrons and holes slowly release due to thermal motion atroom temperature after activation, and combine to release energy,resulting in the afterglow phenomenon. When the materials are heated,the electrons and/or holes in the defect levels will release quickly,causing the materials to emit bright thermoluminescence. Green-lightlong afterglow materials are frequently reported at present, whilereports on the yellow light afterglow materials are few. CN1324109Cdiscloses a Y₂O₂S yellow light afterglow material activated with rareearth activator-free trivalent titanium and a preparation methodthereof, and CN100491497C discloses an alkali earth metal silicate longafterglow luminescent material activated with Eu²⁺. On the basis ofsystematic research on the rare earth long afterglow luminescentmaterial, we put forward and verified such a research and developmentviewpoint on the afterglow luminescent materials: a defect level ofappropriate depth can be created in a luminescent material which doesnot have afterglow property but has excellent luminescent property bybeing purposefully introduced into a defect center, so that the defectlevel can effectively store external luminous energy, and then thestored energy sustainably releases under the action of external thermalexcitation and is transferred to luminescent ions, resulting in theafterglow phenomenon. Most of afterglow luminescent powder reported hasgood afterglow properties by adding coactive ions to the materials toform the defect centers, such as Chinese patents CN1152114C, CN1151988Cand 200610172187.9.

A luminescent material Y₃A1₅O₁₂:Ce³⁺ was reported on page 53, Volume 11of Appl.Phys.Lett. in 1967, the material has yellow luminescence, withthe strongest luminescent wavelength at 550 nm, and fluorescencelifetime less than 100 ns. The realization of LED white light emissionusing yellow luminescence of Y₃A1₅O₁₂:Ce³⁺ and blue light galliumnitride was reported on page 417, No. 64 of Appl.Phys.A in 1997. Y₃A1₅O₁₂:Ce³⁺ was not reported to have afterglow luminescence.

At present, LED is used for illumination, display, backlight and otherfields, and considered as the most promising next generationilluminating pattern for energy conservation, durability, no pollutionand other advantages, and draws extensive attention. Various solutionsare adopted to realize white light LED, among which combination of ablue light LED chip and yellow fluorescent powder for realization of thewhite light emission is the most mature technical solution for preparingthe white light LED at present. However, in practical application,luminescent intensity of the blue light LED chip and the fluorescentpowder will decrease with temperature rise of devices during operation,and decrease in the luminescent intensity of the fluorescent powder ismore significant, affecting the use of the LED. Conventional LED uses DCas driving energy. However, household power, industrial/commercial orpublic power are mostly supplied in AC at present, the LED must beprovided with a rectifier transformer for AC/DC conversion in case ofbeing used for illumination and other applications so as to ensurenormal operation of the LED. In the process of AC/DC conversion, powerloss is up to 15-30%, the cost of conversion equipment is considerable,installation takes a lot of work and time, and the efficiency is nothigh. Chinese patent CN100464111C discloses an AC LED lamp whichconnects LED chips of different emitting colors to AC power supply inparallel, mainly describes that the LED chips of different colors formwhite light and a specific circuit thereof (e.g. red, green and bluelight emitting chips), and does not relate to the luminescent powder.U.S. Pat. No. 7,489,086,B2 discloses an AC LED driving device and ailluminating device using the same, the patent also focuses on circuitcomposition, and the luminescent powder is still the conventionalY₃Al₅O₁₂:Ce³⁺ luminescent powder. So far, realization of AC LED from theluminescent materials has not been reported.

SUMMARY OF THE INVENTION

A technical problem to be solved by the invention is to provide a newyellow light afterglow material, providing a new choice for theafterglow material field, especially the LED technical field.

The yellow light afterglow material of the invention comprises thefollowing chemical formula:

aY₂O₃.bAl₂O₃.cSiO₂:mCe.nB.xNa.yP

where, a, b, c, m, n, x and y are coefficients, and a is not less than 1but not more than 2, b is not less than 2 but not more than 3, c is notless than 0.001 but not more than 1, m is not less than 0.0001 but notmore than 0.6, n is not less than 0.0001 but not more than 0.5, x is notless than 0.0001 but not more than 0.2, and y is not less than 0.0001but not more than 0.5.

The yellow light afterglow material of the invention uses trivalent Ceas luminescent ions, and B, Na and P as a defect center. When excited byultraviolet light and visible light, the material of the invention emitsbright yellow afterglow.

The invention also provides a preparation method of the yellow lightafterglow material, and the method comprises the following steps: evenlymixing raw materials by molar ratio, sintering the raw materials at1200-1700° for 1-8 h in a reducing atmosphere once or several times,preferably at 1400-1600° for 2-5 h.

The invention also provides a DC LED illuminating device using theyellow light afterglow material, and refers to FIG. 1 for schematicdiagram of an LED basic module of the illuminating device. As thematerial of the invention has thermoluminescence effect, the materialcan compensate temperature quenching generated by using the conventionalluminescent powder when the device is at a high operating temperature,maintaining the overall luminescence of the LED illuminating device inoperation at a relatively stable level.

The invention also provides an AC LED illuminating device using theyellow light afterglow material, and refers to FIG. 2 for schematicdiagram of an LED basic module of the illuminating device. It can beseen from the figure that AC input can be realized by connecting tworeverse LEDs in parallel. As the yellow light afterglow material of theinvention has afterglow luminescence characteristics, when the materialis applied to the AC LED illuminating device, afterglow of theluminescent powder can compensate weaker LED luminescence due to currentdrop when current cycle changes, thus maintaining stable light output ofthe device in AC cycle.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an LED basic module of a DC LEDilluminating device;

FIG. 2 is a schematic diagram of an LED basic module of an AC LEDilluminating device;

FIG. 3 is an excitation spectrum of sample 2;

FIG. 4 is a photoluminescence spectrum of the sample 2;

FIG. 5 is an afterglow spectrum of the sample 2; and

FIG. 6 is a thermoluminescence spectrum of the sample 2.

The invention will be further illustrated in detail through preferredembodiments in the form of examples. However, the following examplesshould not be construed as limit to the scope of the invention, andtechnologies realized based on the contents of the invention shall fallinto the scope of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The yellow light afterglow material of the invention comprises thefollowing chemical formula:

aY₂O₃.bAl₂O₃.cSiO₂:mCe.nB.xNa.yP, where a, b, c, m, n, x and y arecoefficients, and a is not less than 1 but not more than 2, b is notless than 2 but not more than 3, c is not less than 0.001 but not morethan 1, m is not less than 0.0001 but not more than 0.6, n is not lessthan 0.0001 but not more than 0.5, x is not less than 0.0001 but notmore than 0.2, and y is not less than 0.0001 but not more than 0.5.

Preferably:

a is not less than 1.3 but not more than 1.8, b is not less than 2.3 butnot more than 2.7, c is not less than 0.001 but not more than 0.5, m isnot less than 0.01 but not more than 0.3, n is not less than 0.01 butnot more than 0.3, x is not less than 0.01 but not more than 0.1, and yis not less than 0.01 but not more than 0.5.

More preferably a is not less than 1.3 but not more than 1.5, b is notless than 2.3 but not more than 2.5, c is not less than 0.01 but notmore than 0.5, m is not less than 0.01 but not more than 0.3, n is notless than 0.1 but not more than 0.3, x is not less than 0.02 but notmore than 0.1, and y is not less than 0.2 but not more than 0.3.

Most preferably:

1.45Y₂O₃.2.5Al₂O₃.0.01SiO₂: 0.24Ce.0.05B.0.1Na.0.2P

or

1.45Y₂O₃.2.5Al₂O₃.0.5SiO₂: 0.01Ce.0.3B.0.02Na.0.3P.

The yellow light afterglow material of the invention uses trivalent Ceas luminescent ions, and B, Na and P as a defect center. When excited byultraviolet light and visible light, the material of the invention emitsbright yellow light afterglow.

The yellow light afterglow material of the invention uses oxides of Y,Al, Si, Ce, Na, B and P or elementary substances and compounds which cangenerate the oxides at high temperature as raw materials.

The preparation method of the yellow light afterglow material comprisesthe following steps: evenly mixing the raw materials by molar ratio,sintering the raw materials at 1200-1700° for 1-8 h in a reducingatmosphere once or several times, preferably at 1400-1600° for 2-5 h.

Further, the yellow light afterglow material of the invention hasexcitation wavelength of 200-500 nm and the strongest emissionwavelength of 530-570 nm. The material can store energy from ultravioletlight and/or visible light, and then emit yellow light afterglow at roomtemperature and emit thermoluminescence when heated, afterglowluminescent and thermoluminescence peak is 530-570 nm, and peaktemperature of thermoluminescence is 60-350°.

Refer to FIG. 1 for schematic diagram of a basic module of a DC LEDilluminating device using the yellow light afterglow material of theinvention. As the LED illuminating device is at 60-200° in use, theluminance of the conventional YAG:Ce³⁺ luminescent powder will decreasedue to higher temperature, therefore, the luminance of the LEDilluminating device decreases and luminescence turns blue. As thematerial of the invention can generate thermoluminescence when heated,and emit yellow fluorescence when excited by blue light LED chips, whitelight LED illumination can be realized by blue light plus yellow lightwhen the material of the invention is used in the LED illuminatingdevice. However, as the material of the invention has thermoluminescenceeffect when the temperature of the device rises, and energy in thedefect center will release in the form of luminescence when heated, thematerial can compensate temperature quenching generated by using theconventional YAG:Ce³⁺ luminescent powder when the device is at highoperating temperature, maintaining the overall luminescence of the LEDilluminating device in operation at a relatively stable level.

Refer to FIG. 2 for schematic diagram of an LED basic module of an ACLED illuminating device using the yellow light afterglow material of theinvention. It can be seen from the figure that AC input can be realizedby connecting two reverse LEDs in parallel. Luminescence realized byconnecting two reverse LEDs in parallel also has periodic luminancechange for periodicity of AC, affecting applications of the device. Asthe yellow light afterglow material of the invention has afterglowluminescence characteristics, when the material is applied to the AC LEDilluminating device, afterglow of the luminescent powder can compensateweaker LED luminescence due to current drop when current cycle changes,thus maintaining stable light output of the device in AC cycle.

The invention will be further described through preferred embodiments,but the following examples should not be construed as limit thereto. Itshould be understood by those skilled in the art that variousmodifications, replacements and changes can be made according to thetechnical thought of the invention.

Examples 1- 12

Yttrium oxide, alumina, silica, cerium dioxide, sodium bicarbonate,boric acid and monoammonium phosphate were fully mixed according to themixture ratio in Table 1, and sintered at 1550° for 4 h in a mixtureatmosphere of hydrogen and nitrogen to obtain a finished product aftercrushing, sieving, pickling and washing with water and alcohol. Then thephosphor was encapsulated into a basic unit such as the DC and/or AC LEDilluminating device as shown in FIG. 1 and FIG. 2 to obtain an LEDilluminating device.

Y_(2.94) Ce_(0.06) Al₅O₁₂ was prepared by the same process route as areference sample.

TABLE 1 Mixture ratio of sample materials (mol) Yttrium Cerium BoricSodium Monoammonium Sample oxide Alumina Silica dioxide acid bicarbonatephosphate Reference 1.47 2.5 0 0.06 0 0 0 sample 1 1.5 2.6 0.01 0.1 0.050.1 0.2 2 1.45 2.5 0.01 0.24 0.05 0.1 0.2 3 1 2.05 0.001 0.0001 0.10.002 0.01 4 1.2 2.2 0.005 0.05 0.06 0.0001 0.08 5 1.85 2.7 0.12 0.0080.0065 0.05 0.004 6 2 2.95 1 0.2 0.3 0.04 0.04 7 1.45 2.5 0.002 0.6 0.150.03 0.3 8 1.45 2.5 0.5 0.01 0.3 0.02 0.3 9 1.45 2.5 0.01 0.3 0.5 0.010.0001 10 1.75 3 0.01 0.34 0.02 0.06 0.4 11 1.15 2 0.014 0.18 0.25 0.0030.26 12 1.4 2.45 0.02 0.15 0.0001 0.2 0.5

Test example 1 Luminescence Temperature Characteristics of the Materialof the Invention

All samples and the reference sample in Table 1 were put in atemperature control heating device, and excited by an LED with emissionwavelength of 460 nm. Luminance was read by a luminance meter atdifferent temperatures. Refer to Table 2 for results.

TABLE 2 Sample 25° C. 80° C. 150° C. 200° C. Reference 100 100 100 100sample 1 99 105 110 110 2 105 110 115 110 3 94 103 110 115 4 93 108 105108 5 93 103 106 106 6 95 105 105 108 7 90 102 106 105 8 102 106 110 1119 106 108 110 109 10  99 110 105 106 11  90 102 103 105 12  98 105 110110

It can be seen from Table 2 that the luminance of the yellow lightafterglow material of the invention is greater than that of currentY_(2.94) Ce_(0.06) Al₅O₁₂ luminescent powder at the operatingtemperature of the LED illuminating device (>80°), thus being capable ofsolving temperature quenching problems of luminance of the existing DCLED illuminating devices.

Test example 2 Afterglow Characteristics of the Material of theInvention

All samples and the reference sample in Table 1 were excited by an LEDwith dominant emission wavelength of 460 nm for 15 minutes, andafterglow thereafter was tested by a glow tester equipped with aphotomultiplier. Refer to Table 3 for results.

TABLE 3 Luminance at Luminance at Luminance at Sample 0 second 30seconds 1 minute Reference 0 0 0 sample 1 100 100 100 2 120 118 116 3 8680 81 4 90 91 90 5 70 74 70 6 65 63 63 7 104 105 106 8 110 112 110 9 8880 81 10  80 85 81 11  75 71 70 12  65 60 65

Luminance values in Table 3 took sample 1 as a reference. Afterglowluminescence value of the reference sample below the lower limit of atesting instrument 1 mcd/m², and can not be read, thus being recorded as0.

FIG. 3 is an excitation spectrum of sample 2, FIG. 4 is aphotoluminescence spectrum of the sample 2, FIG. 3 and FIG. 4 show thatthe material of the invention emits yellow fluorescence when excited byultraviolet to visible light. FIG. 5 is an afterglow spectrum of thesample 2, showing that afterglow luminescence of the material of theinvention is yellow. FIG. 6 is a thermoluminescence spectrum of sample2, showing that the material of the invention has thermoluminescencephenomenon when heated to above 60°.

As frequency of common AC is 50 Hz, that is, the period is 20 ms, thedirection does not change, and change in current is 10 ms persemi-period. Table 5 provides afterglow luminance within 10 ms tested bya high speed CCD capable of taking 300 pictures per second when thesample 2 is excited by an LED with dominant emission wavelength of 460nm for 15 minutes and the excitation stops. Refer to Table 4 forresults.

TABLE 4 3.33 ms 6.66 ms 9.99 ms Reference 2 1 1 sample Sample 2 15271510 1505

It can be seen from Table 4 that the material of the invention hasafterglow luminescence, while the existing Y_(2.94) Ce_(0.06) Al₅O₁₂luminescent powder does not have afterglow luminescence. The figures inTable 4 show that the luminescent material of the invention has strongerafterglow luminescence within the AC cycle, and can effectivelycompensate luminescent intensity loss due to the current drop. Theafterglow value of the reference sample is caused by instrument noise,and can be ignored.

The figures in Tables 2 to 4 show that the material of the invention hasthe afterglow luminescence characteristics compared with the materialY_(2.94) Ce_(0.06) Al₅O₁₂ reported by documents, and the DC and/or ACLED illuminating device of the basic unit (as shown in FIG. 1 and FIG.2) using the yellow light afterglow material of the invention hasobvious novelty and creativity.

1. A yellow light afterglow material, comprising the following chemicalformula: aY₂O₃.bAl₂O₃.cSiO₂:mCe.nB.xNa.yP, wherein a, b, c, m, n, x andy are coefficients, and a is not less than 1 but not more than 2, b isnot less than 2 but not more than 3, c is not less than 0.001 but notmore than 1, m is not less than 0.0001 but not more than 0.6, n is notless than 0.0001 but not more than 0.5, x is not less than 0.0001 butnot more than 0.2, and y is not less than 0.0001 but not more than 0.5.2. The yellow light afterglow material of claim 1, wherein a is not lessthan 1.3 but not more than 1.8, b is not less than 2.3 but not more than2.7, c is not less than 0.001 but not more than 0.5, m is not less than0.01 but not more than 0.3, n is not less than 0.01 but not more than0.3, x is not less than 0.01 but not more than 0.1, and y is not lessthan 0.01 but not more than 0.5.
 3. The yellow light afterglow materialof claim 2, wherein a is not less than 1.3 but not more than 1.5, b isnot less than 2.3 but not more than 2.5, c is not less than 0.01 but notmore than 0.5, m is not less than 0.01 but not more than 0.3, n is notless than 0.1 but not more than 0.3, x is not less than 0.02 but notmore than 0.1, and y is not less than 0.2 but not more than 0.3.
 4. Theyellow light afterglow material of claim 4, comprising a compound havingthe following chemical formula:1.45Y₂O₃.2.5Al₂O₃.0.01SiO₂: 0.24Ce.0.05B.0.1Na.0.2Por1.45Y₂O₃.2.5A10₃.0.5SiO₂: 0.01Ce.0.3B.0.02Na.0.3P.
 5. The yellow lightafterglow material of claim 1, wherein an excitation wavelength of theyellow light afterglow material is from 200 nm to 500 nm, and astrongest emission wavelength is from 530 nm to 570 nm.
 6. The yellowlight afterglow material of claim 5, wherein a thermoluminescence peakof the yellow light afterglow material is from 530 nm to 570 nm, and apeak temperature of thermoluminescence is from 60° to 350°.
 7. A methodfor preparing the yellow light afterglow material of claim 1, comprisingthe following steps: weighing oxides, of elements or materials which cangenerate oxides at high temperature by molar ratio as raw materials; andevenly mixing and then sintering the raw materials at 1200-1700° in areducing atmosphere.
 8. The method for preparing the yellow lightafterglow material of claim 7, wherein a sintering temperature is1400-1600°, and a sintering time is 2-5 h.
 9. A method for preparing anLED illuminating device, said method comprising use of the yellow lightafterglow material of claim
 1. 10. An LED illuminating device,comprising an LED chip and luminescent powder, wherein the luminescentpowder is the yellow light afterglow material of claim 1, and anemission wavelength of the LED chip is 240-500 nm.
 11. The yellow lightafterglow material of claim 4, wherein an excitation wavelength of theyellow light afterglow material is from 200 nm to 500 nm, and astrongest emission wavelength is from 530 nm to 570 nm.
 12. The yellowlight afterglow material of claim 11, wherein a thermoluminescence peakof the yellow light afterglow material is from 530 nm to 570 nm, and apeak temperature of thermoluminescence is from 60° to 350°.
 13. A methodfor preparing the yellow light afterglow material of claim 12,comprising the following steps: weighing oxides of elements or materialswhich can generate oxides at high temperature by molar ratio as rawmaterials; and evenly mixing and then sintering the raw materials at1200-1700° in a reducing atmosphere.
 14. A method for preparing an LEDilluminating device, said method comprising use of the yellow lightafterglow material of claim
 12. 15. An LED illuminating device,comprising an LED chip and luminescent powder, wherein the luminescentpowder is the yellow light afterglow material of claim 12, and anemission wavelength of the LED chip is 240-500 nm.